1. Field of the Invention
The present invention relates to a fluid filled vibration damping device adapted to provide active vibration damping action through control of pressure fluctuations of a pressure receiving chamber filled with a non-compressible fluid, wherein control is carried out in a cycle that corresponds to the frequency of the vibration to be damped.
2. Description of the Related Art
In the field of vibration damping devices such as vibration damping linkages or vibration damping supports designed for installation between components that make up a vibration transmission system, one type of known device is a fluid filled type vibration damping device having a first mounting member and a second mounting member linked by a rubber elastic body; a pressure-receiving chamber whose wall is partially defined by the rubber elastic body and an equilibrium chamber whose wall is partially defined by a flexible film, the pressure-receiving chamber and the equilibrium chamber being formed to either side of a partition member and filled with a non-compressible fluid; and an orifice passage connecting the pressure-receiving chamber and the equilibrium chamber. Since this type of fluid filled vibration damping device is able to exhibit vibration damping effect by using flow action, e.g. resonance action, of fluid flowing through the orifice passage, application of such devices in automotive engine mounts and the like is a current topic of interest.
However, one problem with such devices was that in order to for each of the orifice passages to achieve the orifice effect effectively, each orifice passage is limited to a pre-tuned, relatively narrow frequency range. Thus, in instances where frequency or other characteristic of vibration targeted for damping varies, or where advanced vibration damping action is required, difficultly in achieving satisfactory vibration damping action was a problem.
As one approach to solving this problem, in recent years, vibration damping devices of active type have been developed and are the subject of ongoing research. In such active vibration damping devices, typically, another part of the wall of the pressure-receiving chamber is defined by an oscillating plate, and through actuated oscillation of this oscillating plate at a cycle corresponding to the frequency of the vibration being damped, the pressure in the pressure-receiving chamber is controlled to produce positive and active vibration damping action. One such device is disclosed in U.S. Pat. No. 6,527,262, for example.
In the active type fluid filled vibration damping device disclosed in U.S. Pat. No. 6,527,262, the oscillating plate is linked to a second mounting member via a supporting rubber elastic body of annular shape, with the aim of elastically positioning and supporting the oscillating plate on the second mounting member while maintaining fluidtightness of the pressure-receiving chamber. For this reason, there was a risk that permanent set in fatigue of the supporting rubber elastic body might make it difficult to consistently achieve the desired vibration damping action. Additionally, since oscillation energy of the oscillating plate is consumed through deformation of the supporting rubber elastic body, there is a risk of diminished actuation efficiency of the oscillating plate.
In order to address such problems, it would be conceivable, for example, to employ an oscillating plate of piston construction as taught in Japanese Unexamined Patent Publication Nos. JP-A-06-330980 or JP-A-2005-291276. According to these fluid filled vibration damping devices, a through-hole of cylinder shape is formed in the partition member, a piston shaped oscillating plate is disposed at the distal end side of the output member of the actuator in the actuation direction, and the oscillating plate is movable in the axial direction along the inside peripheral face of the partition member constituting the peripheral wall of the through-hole. The gap provided between the outside peripheral face of the oscillating plate and the inside peripheral face of the partition member obviates the need for the supporting rubber elastic body to support the oscillating plate on the second mounting fitting, thereby solving the aforementioned problem stemming from the support structure for the oscillating plate via the supporting rubber elastic body.
However, a fluid filled vibration damping device furnished with such a piston shaped oscillating plate proved to have the problem that pressure in the pressure-receiving chamber leaks out through the gap between the inside peripheral face of the partition member and the outside peripheral face of the oscillating plate. Specifically, the problem of difficulty in achieving satisfactory orifice effect arose as a result of pressure leaking from the pressure-receiving chamber through the gap and reducing the level of fluid flow through the orifice passage.
The above-mentioned JP-A-06-330980 and JP-A-2005-291276 also teach making the gap sufficiently small in size. However, simply reducing the size of the gap does not readily prevent pressure leakage from the pressure-receiving chamber to a sufficient extent. Moreover, if the gap is too small, the oscillating plate may interfere with the inside peripheral face of the partition member, resulting in the risk of diminished actuation efficiency of the oscillating plate, of scratching or other damage to the opposed faces of the oscillating plate and the cylinder member, or of unwanted noise.